1. Field of the Invention
The present invention relates to a wheel bearing unit for supporting a car wheel of a motor vehicle, and more particularly to a wheel bearing unit for use in a driving wheel that is composed of a combination of a wheel bearing and a constant velocity universal joint acting as a unit.
2. Description of the Related Art
FIG. 5 illustrates the structure of a conventional example of a wheel bearing unit that is composed of a combination of a wheel bearing 1 and a constant velocity universal joint 7 acting as a unit. The wheel bearing 1 is composed of an outer race member 2 which is attached to the body of a motor vehicle, and an inner race member 4 which is rotatably supported through two rows of balls 3 by the outer race member 2. The inner race member 4 is composed of two separate components, of which one is a hub wheel 5 provided with a flange used for mounting of a car wheel and the other is an inner ring 6 engaged with the hub wheel 5.
In the inner race member 4, raceway surfaces 4a and 4b are provided in the hub wheel 5 and the inner ring 6, respectively, so as to face two rows of raceway surfaces 2a and 2b of the outer race member 2, respectively.
The inner ring 6, which is provided with the raceway surface 4b serving as an inner raceway surface as seen from the cross direction of the vehicle, i.e., an inboard raceway surface, is press-fitted to the cylindrical end portion of the hub wheel 5, and therefore it never occurs that the components constituting the wheel bearing 1 are inadvertently disassembled before being assembled into the vehicle, for example, during shipment. Note that, here, one of the shoulders of the raceway groove hasis removed. In the inner ring 6 thus constructed, the outer diameter of the smaller end face is equal to or smaller than the groove-bottom diameter of the raceway groove.
The wheel bearing unit shown in FIG. 5 is constructed in such a manner that the inner ring 6 is first engaged with the hub wheel 5, and the hub wheel 5 is thereafter engaged with the constant velocity universal joint 7. That is, this wheel bearing unit adopts the so-called double engagement construction. Accordingly, the hub wheel 5 tends to have an unduly great wall thickness. If the hub wheel 5 and the inner ring 6 are directly engaged with the constant velocity universal joint 7, respectively, it is possible to reduce the wall thickness of the hub wheel 5 and thereby make it light-weight, or increase the diameter of the spline portion. In this case, however, the hub wheel 5 and the inner ring 6 need to be realized as separate components. This requires that extra measures be taken to prevent the inner ring 6 and the balls 3 from being disassembled inadvertently during shipment, for example, before the separate components are assembled into the constant velocity universal joint 7.
With regard to the above-described matter, for example, in the publication of Japanese Utility Model Application No. Sho 63-180721 a technique to prevent components from being disassembled during shipment is proposed. According to this technique, as shown in FIG. 6A, a cage 8 has a projection 8a formed so as to protrude therefrom in the direction of the internal diameter thereof. The projection 8a is fitted into a groove 9a formed in an inner ring 9. Moreover, as one of commonly-used ball bearings, as shown in FIG. 6B, a construction is known in which a pair of inner rings a are kept non-separable by providing a projection a2 in the vicinity of the groove bottom portion of each inner ring a. In these conventional examples, however, the raceway surface a1, the projection a2, and the smaller end face a3 are separately ground, and therefore the following problem arises.
That is, a radius difference xcex4 between a diameter d1 of the groove bottom portion of the raceway surface a1 and an outer diameter d2 of the projection a2 is equal to an mount of interference required when the inner ring a is assembled in its axial direction. A tolerance of the mount of interference is equal to a sum of a tolerance of the diameter d1 of the groove bottom portion and a tolerance of the outer diameter d2 of the projection a2. Therefore, several tens of xcexcm is required for the tolerance of the amount of interference xcex4. Thus, a variation in the amount of interference xcex4 is so large that there is a great possibility that a pressurized imprint is adversely planted on a ball b. Therefore, it is. necessary to apply heat to an outer ring c to increase the inscribed circle diameter to assemble the inner wheel a. Moreover, a tolerance of a core deviation determining an axialinternal clearance, i.e., the distance between the groove bottom portion and the smaller end face a3, is equal to a sum of a tolerance of the raceway surface a1 and a tolerance of the smaller end face a3. Therefore, if the raceway surface a1 and the smaller end face a3 are separately ground, the tolerance of the core deviation becomes excessively large. Several tens of xcexcm is also required for this tolerance of the core deviation. For this reason, it is not possible to reduce the initial axial gap to a small value, or if the initial axial gap is reduced forcibly, it is necessary to employ a selective assembly method (matching).
The present invention has been conducted in view of the above-discussed problems observed in conventional wheel bearing units. It is an object of the present invention to provide an improved wheel bearing unit in which the set value of the amount of interference is kept constant and a preload variation is satisfactorily suppressed by minimizing the set value of the initial axial gap.
To achieve the above object, a wheel bearing unit according to the present invention comprises:
an outer. race member having two rows of raceway surfaces formed in its inner peripheral surface, the outer race member being attached to the body of a motor vehicle; and
an inner race member provided with a wheel mounting flange, the inner race member being rotatably supported through two rows of balls by the outer race member,
wherein the inner race member has a projection formed in the vicinity of the groove bottom portion of its raceway surface, the projection having a diameter greater than the inscribed circle diameter,
and wherein, in the inner race member, the raceway surface, the outer peripheral surface of the projection, and the smaller end face are concurrently ground to keep within the range of predetermined values the radius difference between the diameter of the groove bottom portion of the raceway surface of the inner race member and the outer diameter of the projection, as well as the core deviation between the groove bottom portion of the raceway surface and the smaller end face.
In this construction, by concurrently grinding the raceway surface, the outer peripheral surface of the projection, and the smaller end face, not only it is possible to reduce the number of man-hours required, but it is also possible to satisfactorily suppress variations in tolerances. This. helps make the range of preload variation narrower. Moreover, at the time. when the raceway surface, the outer peripheral surface of the projection, and the smaller end face are concurrently ground, the shoulder portion (in the inner ring) and the sealing land (in the hub wheel) may be additionally ground concurrently. By doing so, the sealing land of the hub wheel or the outer peripheral surface of the shoulder portion of the inner ring is realized as a ground surface free from lead burrs or tool marks extending circumferentially, and this leads to an improvement of sealability.
According to an embodiment of the invention, in the inner race member, the highest value of the tolerance of the radius difference between the diameter of the groove bottom portion of the raceway surface and the outer diameter of the projection, and the same of the core deviation between the groove bottom portion of the raceway surface and the smaller end face are respectively limited to 20 xcexcm, and more preferably, 10 xcexcm.
The inner race member may be composed of a hub wheel having a wheel mounting flange formed integrally therein, and an inner ring provided separately from the hub wheel. In this construction, the hub wheel has a raceway surface formed so as to face one of two rows of the raceway surfaces of the outer race member, and the inner ring has a raceway surface formed so as to face the other of two rows of the raceway surfaces of the outer race member.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.